The invention relates to mine roof supports.
In the underground mining of coal or like minerals by the longwall method of mining, a strip or web of mineral, for example coal, the thickness of the coal seam and up to 150 meters long is removed from the coal face by a mining machine traversing along the coal face. Because of the undulating nature of such seams, and the need to steer the machine within the seam to follow the undulations, steps are produced in the floor and the roof parallel to the direction of travel of the mining machine. If the steps are small, or the strata is friable, these steps are crushed and have no detrimental effect on the roof supporting function of the mine roof supports which are advanced sequentially behind the mining machine to support the newly exposed mine roof.
In a typical mine, the width of cut of removal of coal from the face may be 1 meter and the roof supporting structure of the mine roof support may be 3 meters long. It can thus be envisaged and demonstrated that the roof supporting structure bridges and contacts a series of steps in the roof in the roof supporting mode. Because the floor engaging structure of a mine roof support is usually shorter than the roof engaging structure the problems are not so acute and are therefore readily accommodated with conventional base structures.